Apparatus for advancing nonmetallic plastic material



194 G. E. HENNING i 2,471,324

"a ay APPARATUS Fon ADVANCING NONMETALLIC PLASTIC MATERIAL Filed Nov. 13, 1946 2 SheebS-Sheet 2 v /A/l/ENTOR i 6.5. HE/v/v/NG A m BV f J`.\ ArroRA/Ey Patented May 24, 1949 UNITED STATES l QFFICE APPARATUS FOR ADVANCING NON- METALLIC PLASTIC MATERIAL Application November 13, 1946, Serial No. 709,47 9

This invention relates to an apparatus for advancing non-metallic plastic material.

In the manufacture of extruded products, such as insulated conductors, plastic material, such as thermoplasticlcompounds or compounds including rubber or synthetic rubber-like mate- -rials, sometimes are milled to thoroughly mix and plasticize the material so that it may be extruded properly. The material then is inserted into an extruder, which extrudes the material upon a conductor, while the material is in a plastic condition. Such working operations are relatively expensive and require considerable handling of the material. In the past, there has been no apparatus for reducing or substantially eliminating the necessity of the working operations prior to the insertion of the material into the extruder.

An `object of the invention isrthe provision of new and improved apparatus for ladvancing nonmetallic lplastic material.

A further object of the invention is the provision of new and improved apparatus for forcing plastic material through extrusion cylinders onto conductors. v

An apparatus illustrative of the invention is provided with an extrusion cylinder having a liner provided with a plurality of longitudinally extending grooves for preventing plastic material from turning with a stock screw rotated therein, whereby the delivery eiciency of the stock screw is increased.

A complete understanding of the invention may be obtained from the following detailed description of an apparatus forming a specic embodiment thereof, when read in conjunction with the appended drawings, in which:

Fig. 1 is a fragmentary, horizontal section of an apparatus forming one embodiment of the invention;

Fig. 2 is a reduced, fragmentary, vertical section of a portion of the apparatus;

Fig. 3 is an enlarged, fragmentary section taken along line 3-3 of Fig. 2, and

Fig. 4 is an enlarged, fragmentary, transverse, vertical section of a portion of the apparatus.

Referring now in detail to the drawings, there is shown in Fig. l an extruder for forming a covering 8 from a non-metallic plastic material, such as a vulcanizable compound including rubber or a synthetic rubber-like material, or a thermoplastic compound, around a lamentary conductor 9, which may be bare or may be covered with a textile or plastic covering. The extruder includes a heated extrusion cylinder I having a bore II in which a stock screw I2 is 2 rotatably mounted. The stock screw is rotated by a shaft I3 (Fig. 2) to force the plastic material under high pressure to an extruding head I4 (Fig. 1).

The extruding head includes a body member l having a tapered opening IS, which forms a continuation of the .bore II and communicates with a bore formed in the extruding head transversely of the tapered opening i6. A strainer I3 is positioned between a rapid discharge section I'I of the bore II and the tapered opening it for straining oversized particles from the material. An annular die holder 2l positioned in the exit end of the bore 20 has a counterbore 22 formed therein in which is mounted a forming die 23.

The conductor 9 is advanced upwardly, as viewed in Fig. 1, by suitable conductor-advancing means, such as a capstan (not shown), through a core tube holder 25 and a core tube 2t, which is held by the core tube holder 25. 1lhe core tube holder is provided with an inclined concave surface 2l for `deflecting the plastic material toward the die l23. An aligning plate 3l maintains the die holder 2l and the core tube holder 25, and thereby the die 23 and the core tube 2S, centered relative to each other in the bore 2B, and a retaining nut 32 holds these elements in the extruding head I4.

The extrusion cylinder IU Vhas a charging opening 4I (Fig. 2) therein for introducing plastic material into the extrusion cylinder. The extrusion screw is provided with a pair of helical threads dil-4I) for advancing the plastic material from the left end, as viewed in Fig. 2, of the bore II to the right end thereof. As the screw I2 is rotated by the shaft I3, the helical threads itl-Jill tend to advance the material toward the right. However, there is a tendency for the material to be revolved by the threads in the bore l I, and if the material would so revolve, it would not be advanced as rapidly toward the right as where the material did not revolve. Substantially longitudinal grooves -45 extending for the major portion of the length of the bore II in long pitch helices directed in the direction of rotation of the screw from left to right, as viewed in Fig. 2, are illled with the plastic material, and tend to prevent the plastic material from being revolved in the bore with the stock screw I2. Since the grooves 45-45 tend to key the material to the cylinder I0, they retard the revolving of the material with the stock screw and the stock screw rotates at a rate of speed relatively greater with respect to the material than if the material revolved with the stock screw thereby advancing the material more rapidly to the right, as viewed in Fig. 2, in the rapid discharge section Il than would l.be the case if the material would be free to revolve with the stock screw. Hence, the delivery efficiency of the stock extruder is increased.

The grooves 45-45 have a slight pitch in a direction opposite to that of the threads l0-l0 so that the material in the grooves is forced therealong during the extrusion operation. Hence, the grooves are constantly being cleared, which might be important where a compound including thermosetting material is extruded inasmuch as clogging of the grooves by thermosetting material is prevented by the self-clearing action oi the grooves. However, the pitch of the grooves is so slight that the keying action of the grooves is not materially aiected.

In the operation of the apparatus described hereinabove, the stock screw I2 is revolved in the bore I I by the drive shaft I3. Plastic material is introduced into the extrusion cylinder I through the opening 4l, and is urged by the stock screw I2 toward the right, as seen in Fig. 2. As the material is urged by the stock screw along the bore I I, it is worked by the stock screw and is plasticized. The substantially longitudinal grooves l5-45 in the rapid discharge section II of the bore II tend to key the material to the extrusion cylinder and prevent revolving of the material with the stock screw. Consequently, substantially all the force exerted by the threads dll-40 on the material is directed toward advancing the material toward the right, as viewed in Fig. 2. The material is forced from the extrusion bore through the strainer I8 into and through the extruding head I4, which forms the material into the covering 8 (Fig. 1) on the conductor 9.

The longitudinal grooves 45-45 (Fig. 2) markedly increase the delivery efficiency of the extruder so that a much larger quantity of plastic material per unit of time may be forced through the rapid discharge section I1 of the bore II for a given rate of rotation of the stock screw I2 than would be the case if the grooves 45-45 were not present. The grooves I5-45 are smal-1 enough in depth that slippage of the material over the threads 40-40 of the stock screw I2 is negligible, but are large enough to substantially retard revolution of the material. The slight helical direction of the grooves -45 aids in forcing the material along the grooves, which action might be important where thermosetting material is extruded by the apparatus in order to prevent setting of the material in the grooves.

What is claimed is:

An apparatus for advancing non-metallic plastic material, which comprises an extrusion cylinder having a bore formed therein, a stock screw positioned in the bore and having threads extending helically in a predetermined direction therearound, and means for rotating the stock screw to advance plastic material through the extrusion cylinder in a predetermined direction, said extrusion cylinder being provided with a plurality of internal grooves extending along a predetermined portion thereof, said grooves being slightly helical in a direction opposite to that of the threads of the stock screw so that the material in the grooves is forced therealong, said grooves serving to prevent revolution of the plastic material with the stock screw and thereby increasing the delivery efficiency of the stock screw.

GEORGE E. HENNING.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,403,681 Gordon Jan. 17, 1922 1,718,893 Brown June 25, 1929 2,200,997 Royle May 14, 1940 FOREIGN PATENTS Number Country Date 568,579 France 1924 

